As I said, there's no issues on my side using a new and fresh MS account. I unfortunately cannot repro the problem you are describing so I cannot help. I know Brasten is trying hard to, but to be honest this login issue is way older than this, there has been people with that problem since over 6 month. Will try to dig further. The solution is to put your Project Spark offline in which case it will work, but you won't have access to UGC

PulseSnK lets take some of that trouble shooting off into a different thread. I was never able to find a solution, but everyone I tried to help never gave me any feedback either, they just vanished on me.

On Windows 10, if you already owned Project Spark before May 13th, you may go into the store, get into your Library, and under the game category, click show all, you can install project spark from there. Only works on accounts that already owned Project Spark. Make sure your PC is up to date, especially drivers, or the game will show in "cannot work on this devices" and the error will be to check for minimum requirements (usually graphics card drivers that need to be installed on a fresh windows installation)